Chondroitin is a polysaccharide comprising a repeated structure of disaccharides of a glucuronic acid (GlcUA) residue and a N-acetyl-D-galactosamine (GalNAc) residue (-GlcUAβ(1-3)-GalNAcβ(1-4)-; in the present specification, also referred to as a chondroitin carbohydrate backbone). Chondroitin sulfate is a polysaccharide which consists by sulfation of chondroitin.
Conventionally, chondroitin and chondroitin sulfate are extracted and purified from cartilages, organs, and the like of animals. However, in recent years, a technique for artificially synthesizing a carbohydrate backbone common to chondroitin and chondroitin sulfate has been studied because of shortage of such materials as cartilages and organs.
Chondroitin synthases, which produce chondroitin by alternately transferring GlcUA and GalNAc from their donor substrates to acceptor oligosaccharides, have been reported, and a method of producing chondroitin using the enzyme has been proposed.
J. Biol. Chem. 275(31), 24124-24129 (2000) discloses a chondroitin synthase derived from Pasteurella multocida. 
In addition, WO 2003/102193 and WO 2003/102194 disclose chondroitin synthases derived from human.
Moreover, U.S. 2003-0109693 (JP 2003-199583 A) discloses a novel chondroitin synthase (KfoC) produced by Escherichia coli K4 strain.
However, in the case of producing chondroitin by the enzymatic methods, it is necessary to prepare expensive materials such as oligosaccharides as acceptors and sugar nucleotides for donors of GlcUA and GalNAc, and thus a method of producing chondroitin using more inexpensive materials has been desired.
Escherichia coli K4 strain is known to produce a polysaccharide having a chondroitin backbone structure as a capsule. However, its structure consists of a repeating unit comprising trisaccharides of a GalNAc residue, a GlcUA residue and a fructose residue that is bound to a C3-hydroxyl group of a GlcUA residue. In addition, over 100 chemically different capsular polysaccharides have been detected in Escherichia coli. For example, Escherichia coli K5 strain produces a capsule polysaccharide K5 which has a carbohydrate backbone of heparin/heparan sulfate (J. Biol. Chem., 272(5), p 2682-2687, 1997). However, the existence of Escherichia coli which produces chondroitin itself has not been known. Therefore, a method of producing chondroitin using an Escherichia bacterium is unknown.
Although US Published Patent Application 2007-0281342 discloses a method of producing chondroitin by using a recombinant gram-positive Bacillus bacterium introduced with a chondroitin synthase gene derived from Pasteurella multocida, further development in fermentative production of chondroitin has been desired.